PROJECT SUMMARY Approximately 2 million units of platelet (PLT) concentrate (PC) are transfused in the U.S. every year to treat or prevent bleeding complications. A typical PC unit collected via apheresis contains a therapeutic dose of PLTs suspended in 200-400mL of plasma. The residual plasma is needed to maintain PLT viability during storage but has no therapeutic value and can be harmful to some patients. Plasma is therefore often removed from PC units to reduce transfusion volume in order to prevent transfusion associated circulatory overload in very young patients (fetuses, neonates) or in adults needing multiple PLT transfusions. PC units are `washed' to replace plasma with isotonic media to prevent adverse outcomes in patients with a history of severe allergic reactions to plasma proteins, infants with neonatal alloimmune thrombocytopenia, and in cases of ABO non-identical transfusions. PC washing may also reduce the risk of transfusion-related acute lung injury, and early mortality in acute promyelocytic leukemia. In current practice, PC units are volume-reduced using a large-capacity centrifuge, or washed using a centrifugation-based automated cell processer, by a hospital blood bank. Centrifugation, however, subjects PLTs to substantial shear forces and physical compaction during pelleting, which decreases PLT quality (as indicated by drastically increased activation, reduced aggregability, distorted shape, and release of granule contents). This proposal will establish the feasibility of using novel high- throughput microfluidic technology known as `controlled incremental filtration' (CIF) for volume-reduction and/or washing of PC, without the significant loss of PLT quality and logistical limitations associated with conventional centrifugation-based processes. We have previously developed several CIF-based devices for leukoreduction and concentration of platelets from platelet-rich plasma, with minimal activation, at practical volumetric throughputs, within a very compact footprint. Here we will demonstrate the feasibility of this approach by completing two complementary aims with scope ranging from iterative design optimization and validation work, to testing the quality of volume-reduced and washed PLTs produced by the prototype CIF-based filtration module. First we will optimize the CIF design parameters to (i) maximize the ability of a device to concentrate PLTs with activation and recovery metrics superior to those of centrifugation, and (ii) further expand the capability of the CIF module to also remove residual leukocytes and existing PLT clumps from the stored PC product. Second, we will evaluate the effect of volume-reduction and washing with the CIF device prototype on PLT quality in a split-unit study, using conventional centrifugation-based volume-reduction and washing (in normal saline) as controls. By completing this research, we will develop a functional prototype and generate sufficient in vitro data to support further comprehensive studies of in vivo survival and therapeutic efficacy of PLTs processed using this new centrifugation-free approach.